The most widely used well completion technique for extracting resources from unconventional, tight oil and gas formations, and geothermal energy extraction employs hydraulic fracturing. Hydraulic fracturing utilizes a solution of water, additives, and proppants (sand or man-made ceramic media) that create a long fracture in the shale or rock to enhance and extend natural fractures and thereby increase well productivity. Ideally, the fracture network is as interlinked as possible to natural fractures and is held open against closure forces by proppants. Proppants normally consist of silica-based sands or bauxite (aluminosilicate) materials that are pumped in with the working fluid that serves to hold the fracture surfaces open so that oil or natural gas can flow back into the well for removal. Larger proppant particles are used to increase permeability, while higher strength materials enable the proppants to withstand higher closure stresses. Because the proppants are fairly dense (2.8-3.6 g/cc), the proppants tend to settle out (particularly larger proppants) in the well. Chemical additives are typically added to alter the viscosity of the working fluid to better distribute the proppants, thus greatly increasing friction and pumping costs. Smaller and lighter proppants, combined with improved control over the development of fracture networks, are needed to improve the economics of water, and chemical use in extracting geothermal energy, oil and gas resources from the earth's lithosphere.
Hydraulic fracturing has revolutionized energy production from domestic resources, including tight oil and gas formations, and for unlocking geothermal energy. Hydraulic fracturing was first used in the 1940s, but has since evolved and now is an important technique in the development of oil and gas reserves. Combined with directional drilling, hydraulic fracturing has also demonstrated applications in enhanced geothermal energy (EGS). According to Tester, et al., EGS is estimated to be over 13 million exojoules (EJ), which, with technology improvements, could lead to an extractable recovery of 200,000 EJ's, or roughly 2000 times the annual energy needs of the United States. Continued development of methods to control the development and permeability of fracture networks in tight and hard rock is essential to the continued development of enhanced geothermal energy, as well as oil and gas reserves.
The development of unconventional oil and gas (particularly gas) resources, as well as geothermal energy remains very expensive, and requires the use of large volumes of water. Reducing the cost and water usage for completion operations in hydraulic fracturing is important for continued development of unconventional energy resources.